Lift pump control systems are used for a variety of purposes including vapor management, injection pressure control, temperature control, and lubrication. In one example, a lift pump supplies fuel to a high pressure fuel pump that provides a high injection pressure for direct injectors in an internal combustion engine. The high pressure fuel pump may provide the high injection pressure by supplying high pressure fuel to a fuel rail to which the direct injectors are coupled. A fuel pressure sensor may be disposed in the fuel rail to enable measurement of the fuel rail pressure, on which various aspects of engine operation may be based, such as fuel injection. Degradation in the fuel rail pressure sensor and/or lift pump may cause the fuel rail pressure to deviate from a desired or expected fuel rail pressure, which in turn may result in the injection of undesired fuel quantities, degrading engine operation.
U.S. Pat. No. 7,832,375 discloses systems and methods for addressing fuel pressure uncertainty during engine startup. In particular, a fuel rail pressure sensor may be determined to be in a degraded state if the sensor indicates a fuel rail pressure that deviates from an estimated fuel rail pressure by a predetermined amount. In some examples, the estimated fuel rail pressure is determined based on a lift pump pressure. In response to determining that the fuel rail pressure sensor is operating in a degraded state, the fuel rail pressure may be increased by appropriately operating high and low pressure fuel pumps.
The inventors herein have recognized an issue with the approach identified above. Under some conditions, a difference between a fuel rail pressure measured by a fuel rail pressure sensor and an estimated fuel rail pressure may be the result of degradation in a lift pump, alternatively or additionally to degradation in the fuel rail pressure sensor. Degradation in the operation of a pressure relief valve may also contribute to such a difference. This difference may manifest as the measured fuel rail pressure being less than the estimated fuel rail pressure by a threshold, for example. As such, differences between measured and estimated fuel rail pressures may be interpreted incorrectly, potentially leading to actions being taken that are not intended for the actual cause of the differences.
One approach that at least partially addresses the above issues includes a method of operating a fuel system, comprising applying a pulse to a fuel pump responsive to detecting that lift pump pressure corresponds to a fuel vapor pressure, ceasing application of the pulse responsive to detecting that the lift pump pressure corresponds to a relief setpoint pressure, and indicating degradation in the fuel system if the detected lift pump pressure deviates from an expected lift pump pressure, including distinguishing among degradation in the fuel pump, a lower pressure fuel pressure sensor, a fuel rail pressure sensor, and a pressure relief valve.
In a more specific example, the expected lift pump pressure is determined based on a voltage supplied to the lift pump and a fuel flow rate.
In another aspect of the example, the expected lift pump pressure is the fuel vapor pressure.
In yet another aspect of the example, the expected lift pump pressure is the relief setpoint pressure, and indicating degradation in the fuel system includes, if the detected lift pump pressure exceeds the relief setpoint pressure, assuming a fault in a lower pressure fuel pressure sensor, the fuel rail pressure sensor, and/or the pressure relief valve, and if the detected lift pump pressure is less than the relief setpoint pressure, assuming a fault in the fuel rail pressure sensor, the lower pressure fuel pressure sensor, the pressure relief valve, and/or the fuel pump.
In this way, the cause of degradation in a fuel system can be definitively identified and compensated. Thus, the technical result is achieved by these actions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.